1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a method of call processing in a Call State Control Function (CSCF) in a third generation Internet Protocol (3G.IP) network.
2. Description of Related Art
In second generation (2G) radio telecommunications networks, each type of call setup message is associated with a specific function and has specific properties that trigger predetermined responses from any Mobile Switching Center (MSC) that receives one of the messages. For example, an originating Mobile Switching Center (MSC) that receives an originating call request from a Mobile Station (MS) automatically performs a number analysis on the called number. If the called number is a mobile number, the originating MSC interrogates the Home Location Register (HLR) associated with the called number to determine the mobile subscriber""s current location. When the location is determined, the HLR sends a Routing Request (ROUTREQ) message to the Visited MSC where the called subscriber is located. The ROUTREQ is a different type of call setup message, and when the ROUTREQ message is received in the Visited MSC, it indicates to the Visited MSC that a call is being placed to a particular MS that is located in the Visited MSC""s service area. The Visited MSC""s response to the ROUTREQ message is to page for the called MS because it is already known that the called subscriber is located there. Thus, none of the MSCs are required to determine their relationship to the called subscriber because each of the call setup messages is specific to a known set of circumstances, and each message has a predetermined response and actions to be performed.
In the 3G.IP networks currently being designed, MSC functions are performed by Call State Control Functions (CSCFs). In addition, call setup messages such as the Fast Setup message and the Location Request (LRQ) message for H.323, and the INVITE message for the Session Initiation Protocol (SIP), do not have properties that indicate to a CSCF receiving them what call processing functions should be performed. Therefore, call processing cannot continue until the CSCF determines what call processing functions it should perform. The present invention provides a CSCF and method by which any CSCF receiving a call setup message can determine what call processing functions it should perform.
In one aspect, the present invention is a method of processing a call to a called mobile station (MS). The method is performed in a Call State Control Function (CSCF) in a third generation Internet Protocol (3G.IP) network. The method begins when an incoming call setup message is received in the CSCF. The call setup message includes an identifier of the called MS, so the CSCF can determine with a relationship function, whether the CSCF is a Home CSCF for the called MS, a Serving CSCF for the called MS, or neither a Home CSCF nor a Serving CSCF for the called MS. The CSCF then selectively performs different call processing steps depending on the result determined by the relationship function.
In another aspect, the present invention is a CSCF in a 3G.IP network for processing a call to a called MS. The CSCF includes means for receiving an incoming call setup message that includes an identifier of the called MS; a relationship function that determines whether the CSCF is the Home CSCF for the called MS, a Serving CSCF for the called MS, or neither a Home CSCF nor a Serving CSCF for the called MS; and means for selectively performing different call processing steps depending on a result determined by the relationship function.
In yet another aspect, the present invention is an all-IP network in which call processing of a call to a called MS is performed by a plurality of CSCFs. The network includes a Home Subscriber Server (HSS) that stores location information for the called MS, a location server that stores a transport address for the called MS, and a Domain Name Server (DNS) that stores an address for a Home CSCF for the called MS. A relationship function is implemented in each of the plurality of CSCFs, and determines whether any CSCF that receives a call setup message is the Home CSCF for the called MS, a Serving CSCF for the called MS, or neither a Home CSCF nor a Serving CSCF for the called MS. Each CSCF also includes defined call processing functions that are selectively performed, depending on a result determined by the relationship function.